Alternating current generator having a plurality of independent three-phase windings

ABSTRACT

There is provided an alternating current generator comprising: a rotatably supported field rotor having a pair of opposed rotor pole cores, each being provided with P/2 claw poles wherein P is an even number, and a field winding wound on the rotor pole cores; an armature core located around the outer periphery of the field rotor and having axially extending 3nP slots wherein n is an integer more than one; n independent sets of three-phase windings, each being wound on the armature core by being inserted in the slots so that the n sets of three-phase windings are shifted from each other by electrical angle of π/(3n) radians; and three-phase rectifiers connected with the n sets of three-phase windings to rectify output voltages generated by the three-phase windings.

BACKGROUND OF THE INVENTION

The present invention relates to an alternating current generator havinga plurality of sets of armature windings. More particularly, thealternating current generator of the present invention is suitable foruse in a vehicle.

There have been used an alternating current (hereinafter referred to asa.c.) generator for a vehicle in which a rotor having field windings isdisposed inside a stator having three-phase windings.

In this case, in order to increase the number of poles, a rotor isprovided on the outer periphery thereof with a plurality of claw-shapedpoles formed on a pair of magnetic cores. The armature of a stator isprovided with 3 P slots (grooves) (one slot per phase and per pole) forthe number of phases of the windings 3 and the number of poles P. Theabove-mentioned three-phase windings are disposed in these grooves and atooth-shaped core is formed between a pair of neighboring slots orgrooves.

However, since the a.c. generator for a vehicle having the claw poleshas one set of three-phase winding and 3P slots (namely, one slot perphase and per pole), a magnetic flux 104 formed between poles 101 and102 leaks through a tooth-shaped core 103 between two windings A asshown in FIG. 9a, when the poles 101, 102 of the rotor and thetooth-shaped core 103 of the armature take a relative position as shownin FIG. 8.

Such leakage of magnetic flux not only reduces the effective magneticflux which contributes to electric power generation, but also generatespulsating magnetic flux.

Accordingly, this causes a magnetic noise to be increased, a generatedvoltage to fluctuate and an output waveform to be distorted, giving riseto ripples when a generated output is rectified into a direct current(hereinafter referred to as d.c.).

It has been demanded that such a magnetic noise is reduced all the morein a power source for a vehicle, etc. which power source feeds variouselectrical equipment utilizing electronic components and ICs. Further, ahigh quality direct current power source having less noise and voltagefluctuation due to a ripple, etc. is demanded.

SUMMARY OF THE INVENTION

It is an object of the present invention is provide an a.c. generator,in which a magnetic noise is reduced and which generates a d.c.rectified output having a stabilized voltage, by reducing leakagemagnetic flux occurring in an a.c. generator.

The inventors have found that it is useful to increase magneticresistance of a magnetic path for the leakage magnetic flux 104 in orderto decrease the leakage of magnetic flux and further that it is usefulto split the tooth-shaped core 103 between the slots as shown in FIG.9b. The inventors have found further that the leaked magnetic flux 104′can be utilized as effective magnetic flux interlinked with windings byinserting separate armature windings A′ in the slots formed in the splittooth-shaped cores as shown in FIG. 9c and that a resultant rectifiedoutput can be stabilized.

Based on the findings, there is provided an alternating currentgenerator comprising a rotatably supported field rotor having a pair ofopposed rotor pole cores, each being provided with P/2 claw poleswherein P is an even number; an armature core located around the outerperiphery of the field rotor and having axially extending 3nP slotswherein n is an integer more than one; n independent sets of three-phasewindings, each being wound on the armature core by being inserted in theslots so that the n sets of three-phase windings are shifted from eachother by electrical angle of π/(3n) radians; and three-phase rectifiersconnected with the n sets of three-phase windings to rectify outputvoltages generated by the three-phase windings.

In a preferred embodiment of the present invention, each of the clawpoles has a trapezoidal peripheral shape and P=12 and n=2 hold, so thatthe armature core has 72 slots and has first and second sets ofthree-phase windings wound thereon.

In accordance with the present invention, less magnetic flux flowsbetween adjacent field poles through the same tooth-shaped core, and aperiod of time during which magnetic flux leaks through the tooth-shapedcore is shortened. Accordingly, an amount of reduction in effectivemagnetic flux for the windings of a stator caused by the leakagemagnetic flux decreases, which makes pulsation of magnetic fluxdifficult to occur. Hence, the fluctuation of a generated voltage andthe distortion of an output waveform are reduced, resulting instabilization of a d.c. rectified voltage.

It is another object of the present invention to reduce a windage noisegenerated by coil ends of armature windings and also to suppressexcessively close assembly of the coil ends.

To accomplish this object, in accordance with the present invention,first and second sets of three-phase windings are inserted in odd andeven numbered slots of the armature core, respectively, and centerportions of the coil ends of each planes of the first and second sets ofthree-phase windings projecting on both sides of the armature core arearranged with a pitch pattern of 1, 2, 2, 3, 2, 2 time as large as aunit pitch in a peripheral direction of the armature core.

In such an arrangement, excessive congregation of the coil ends can beprevented so that necessity of forced bending and radial or axialoverhang of the coil ends for avoiding such excessive congregation ofthe coil ends can be decreased. Since the dispersion of the coil ends ina peripheral direction is uniformed, the level of a noise (a fan noise)at a given audio frequency can be reduced. Since the coil ends aredisposed with unequal pitches in a peripheral direction of the armaturecore, the frequency spectrum of the fan noise becomes broader ascompared with a case in which the coil ends are arranged with an equalpitch, and, since the auditory sensitivity at the reference frequency isshifted to a lower frequency region, it becomes possible to reduce thelevel of an acoustic noise.

It is a further object of the present invention to suppress a magneticnoise and also to reduce the ripple content of a direct current producedby rectifying an a.c. voltage.

In order to serve this purpose, both sets of three-phase windingsinserted in the above-mentioned 3nP slots are connected in Y-form, eachset of three-phase windings is connected with each independentthree-phase rectifier, and d.c. output terminals of respectivethree-phase rectifiers are connected in parallel with each other.

With the above-described configuration, it is possible to effectivelyreduce leakage magnetic flux and also to reduce the ripple content of ad.c. output by virtue of a phase shift between the output voltage ofrespective sets of three-phase windings by a predetermined amount.

It is a still further object of the present invention to reduce anelectromagnetic noise and the number of rectifiers by shifting thedistribution of a resultant magnetomotive force of each phase of thearmature windings with the rotational movement of the rotor.

In order to accomplish this object, two sets of three-phase windings,including a set of Y-connected windings and a set of delta-connectedwindings, are used. The number of turns of the delta-connected windingsis 1.5 to 2.5 times as many as that of the Y-connected windings. The twosets of three-phase windings are connected in parallel with each otherand are connected to a common three-phase rectifier.

With such an arrangement, the distribution of a resultant magnetomotiveforce of each phase of the armature windings is shifted maintaining anon-varying shape, so that no large pulsating vibrational force isgenerated between the rotor and the stator. Therefore, anelectromagnetic noise can be reduced, without giving rise to degradationof output performance and a rise in cost and in size of a product.Furthermore, no unbalanced circulating current is generated between thetwo sets of three-phase windings, so that both sets of three-phasewindings can be connected in parallel with each other and further can beconnected to a common three-phase rectifier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an embodiment of an alternator of thepresent invention;

FIG. 2 is a perspective view showing a rotor in the present embodiment;

FIG. 3 is a lateral development view showing an armature core in thepresent embodiment;

FIG. 4 is a schematic diagram illustrating an armature;

FIG. 5 is a planar development view illustrating the relation betweenthe armature and the magnetic poles;

FIG. 6 is a circuit diagram showing a power supply circuit for a vehicleemploying the alternator of the present embodiment;

FIG. 7 is a waveform diagram showing the waveform of output voltages ofthe alternator of the present embodiment;

FIG. 8 is a planar development view illustrating the relation between anarmature and magnetic poles of the prior art;

FIGS. 9a, 9b and 9c are explanatory diagrams for explaining theoperation and effects of the present invention;

FIG. 10 is a development view of main parts showing another windingsystem;

FIG. 11 is a winding diagram showing the armature windings of a secondembodiment of the present invention;

FIG. 12 is a circuit diagram showing the connection of armaturewindings;

FIG. 13 is a sectional view showing main parts of the generator;

FIG. 14 is a winding diagram for the armature windings showing a stateof congregation of the coil ends according to the winding system of thesecond embodiment;

FIG. 15 is a winding diagram for the armature windings showing a stateof excessive congregation of the coil ends according to the windingsystem in a comparative example;

FIG. 16 is a winding diagram showing the armature windings of a thirdembodiment;

FIGS. 17 through 20 are diagrams showing a fourth embodiment in detail;

FIG. 17 is a circuit diagram showing the connection of the armaturewindings of the third and fourth embodiments;

FIGS. 18a, 18b and 18c are winding diagrams showing a development ofarmature windings of each phase.

FIG. 19 is a side view showing the magnetic poles of a rotor;

FIGS. 20a, 20b, 20c, 20d, 20e, 20f, 20g, and 20h are explanatory viewsshowing the distribution of the air gap magnetomotive force of thearmature windings of each phase;

FIG. 21 is a circuit diagram showing the electric circuit of athree-phase a.c. generator of a fifth embodiment of the presentinvention; and

FIGS. 22a, 22b, 22c, 22d, 22f, 22g, and 22h are explanatory viewsshowing the distribution of the air gap magnetomotive force of thearmature windings of each phase of a prior art three-phase a.c.generator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An a.c. generator for a vehicle proposed by the present invention willnow be described with reference to the embodiments of the presentinvention.

FIG. 1 shows an alternator 1 of the present embodiment. A rotor 10 issupported rotatably within a frame 2 by bearings 3, 4 so that it isrotatable relative to the frame 2. A substantially cylindrical armature(stator) 20 is disposed outside the rotor 10 so that it surrounds therotor 10.

As shown in FIG. 2, the rotor 10 has a rotary shaft 11 which is drivento rotate by an engine (not shown) through a belt (not shown), rotorcores 12, 13 into which the rotary shaft 11 is fitted, and a rotor coil14 which is wound on the rotor cores 12 and 13 to serve as a magneticfield coil. The rotor cores 12 and 13 are provided with integrallyformed claw-shaped magnetic poles 12a and 13a (having a trapezoidalperipheral shape as viewed in the circumferential direction) at theouter peripheral portions thereof, respectively. The rotor cores 12 and13 comprises 6 magnetic poles 12a and 13a, respectively, and themagnetic poles 12a and 13a are alternately disposed along the outerperiphery of the rotor 10.

The armature 20 has an armature core 20a, as shown in FIG. 3, which isformed to have a substantially cylindrical shape by laminating platecores obtained by stamping to form tooth-shaped cores 21a through 26aand slots 21 through 26 disposed therebetween, and armature coils 30,with one inserted in each one of the slots 21 through 26.

In the present embodiment, the armature core 20a is provided with 72slots and 72 tooth-like cores so that two sets of three-phasealternating currents are obtained by 12 magnetic poles of the rotor 10.As shown in FIG. 4, as the armature coil 30, three-phase primary coils31, 32 and 33 an three-phase subsidiary coils 34, 35 and 36 are disposedwithin the slots 21, 23 and 25 and the slots 22, 24 and 26, respectivelyto provide a phase difference of electrical angle 60° with each other.Each of the subsidiary coils 34, 35 and 36 are disposed relative to eachof primary coils 31, 32 and 33 to provide a phase difference ofelectrical angle 30°.

FIG. 5 is a planar development view showing the relative positions ofthe tooth-shaped cores 21a and the magnetic poles 12a, 13a of the rotor10.

In such an arrangement, even when the tooth-like core 21a simultaneouslyoverlaps with the magnetic poles 12a and 13a of the rotor 10 as shown inFIG. 5, the overlap of the tooth-like core 21a with each of the magneticpoles 12a and 13a is very small. In order to reduce the overlappingportion, it is desirable to reduce the length L of the base side of eachof the trapezoidal magnetic poles 12a and 13a to be smaller than 7τ−A,where & denotes a slot pitch and A denotes the peripheral width of a tipend of each tooth-shaped core.

Therefore, magnetic flux formed between the poles 12a and 13a throughthe tooth-like core 21a at this time becomes very little, and theleakage magnetic flux can be suppressed.

As a result, the disturbance in the magnetic flux intersecting each ofthe primary coils 31 through 33 can be suppressed. Since such leakagemagnetic flux in each of the other tooth-like cores 22a through 26a issimilarly reduced, the disturbance in the magnetic flux intersecting thesubsidiary windings 34 through 36 can be suppressed.

In the alternator 1 of the present embodiment having the above-describedstructure, the primary coils 31 through 33 and the subsidiary coils 34through 36 in the armature coil 30 are connected in Y-form and areconnected with rectifiers 5 and 6, respectively. The outputs of therectifiers are supplied to a vehicle battery 7 and a vehicle load 8, andare supplied to a voltage regulator 9 which operates to regulate thevehicle battery at a constant terminal voltage by performing conductioncontrol of the rotor coil 14 in response to the terminal voltage of thevehicle battery.

The thus-constructed alternator 1 generates electric power dependingupon the vehicle load 8 when the rotor 10 is driven by an rotatingengine.

At this time, the primary coils 31 through 33 and the subsidiary coils34 through 36 in the armature coils 30 produce output voltages havingwaveforms represented by a solid line A and a dotted line B in FIG. 7,respectively. Since the subsidiary coils 34 through 36 are arranged inrelation to the primary coils 31 through 33 to have a phase differenceof electrical angle 30°, the resultant voltage V which is obtainedthrough three-phase full rectification by the rectifiers 5 and 6 has awaveform represented by a solid line C in FIG. 7.

The resultant voltage V represented by the solid line C has a differencebetween a maximum voltage and a minimum voltage, that is a ripple, whichis smaller than that of a single voltage waveform represented by adotted line D which is obtained by rectifying the voltage generated onlyby the primary coils 31 through 33.

The difference Veq (=V_(max)−V_(min)) between the maximum voltageV_(max) and the minimum voltage V_(min) is represented as follows:$\begin{matrix}{{Veq} = \quad {{E\left\{ {{\sin \left( {2{\pi/3}} \right)} - {\sin \left( {{- 2}{\pi/3}} \right)}} \right\}} -}} \\{\quad {E\left( {{\sin \left( {{\pi/12} + {2\quad {\pi/3}}} \right)} - {\sin \left( {{\pi/12} - {2{\pi/3}}} \right)}} \right\}}} \\{= \quad {{E\left( {\sqrt{3} - 1.673} \right)} = {0.059\quad E}}}\end{matrix}$

wherein E denotes a maximum value of a sinusoidal wave generated by thearmature coils 30.

The average value {overscore (V)} of the resultant voltage V isrepresented as follows: $\begin{matrix}{\overset{\_}{V} = \quad {\frac{1}{\pi/12}{\int_{0}^{\pi/12}\left\{ {{E\quad {\sin \left( {\theta + {2\quad {\pi/3}}} \right)}} - {E\quad {\sin \left( {\theta - {2\quad {\pi/3}}} \right)}}} \right\}}}} \\{= \quad {1.712\quad E}}\end{matrix}\quad$

The ripple factor Veq/{overscore (V)} is determined as follows:

Veq/V=0.034

In contrast thereto, a conventional a.c. generator for a vehicle havingno auxiliary coil, which is provided with one slot per phase, per poleand is provided with only one set of three-phase coils as the armaturecoil, produces a resultant voltage V represented by a dotted line D inFIG. 7. In this case, the difference Veq between the maximum valuev_(max) and the minimum value v_(min) (=v_(max)−v_(min)) is representedas follows: $\begin{matrix}{{Veq} = \quad {{E\left( {{\sin \left( {2{\pi/3}} \right)} - {\sin \left( {{- 2}{\pi/3}} \right)}} \right\}} -}} \\{\quad {E\left( {{\sin \left( {{\pi/6} + {2{\pi/3}}} \right)} - {\sin \left( {{\pi/6} - {2{\pi/3}}} \right)}} \right\}}} \\{= \quad {{E\left( {\sqrt{3} - {3/2}} \right)} = {0.232E}}}\end{matrix}$

wherein E denotes a maximum value of a sinusoidal wave generated by thearmature coils 30.

The average value {overscore (v)} of the resultant voltage v isrepresented as follows: $\begin{matrix}{\overset{\_}{V} = \quad {\frac{1}{\pi/6}{\int_{0}^{\pi/6}\left\{ {{E\quad {\sin \left( {\theta + {2{\pi/3}}} \right)}} - {E\quad {\sin \left( {\theta - {2{\pi/3}}} \right)}}} \right\}}}} \\{= \quad {{6/\pi} \cdot {\sqrt{3}/2} \cdot E}} \\{= \quad {1.654E}}\end{matrix}$

The ripple factor veq/{overscore (v)} is determined as follows:

veq/v=0.14

Accordingly, it is clear that the ripple factor can be remarkablyreduced in the present embodiment as compared with that obtained by aconventional generator.

As a result, since the ripple in the rectified output voltage isreduced, a high quality d.c. power supply having less voltagefluctuation can be obtained.

Although the armature windings of the present embodiment are connectedin Y-form, they may be connected in delta-form.

Further, as shown in FIG. 10, a plural number of armature windings maybe grouped in one bundle, and the armature windings may be wound inwave-shape and may be wound separated in two layers. In this case, thewinding manufacturing operation becomes easier.

A second embodiment of the present invention will be described withreference to FIGS. 11 to 13.

An a.c. generator is generally provided with a cooling fan radiallyinside of the coil ends of the armature windings projecting on bothsides of the armature core (that is, radially inside of the portions ofthe three-phase armature windings projecting from slots of the armaturecore) so that the coil ends are forcibly cooled by an air flow producedby the fan.

However, the space between the fan and the coil ends is considerablynarrow, so that the action caused by the air flow pressure generated bythe fan upon the narrow space is apt to give rise to a fan noise. Inparticular, since the coil ends of the armature windings have a concaveand convex shape having a predetermined pitch, a noise having a givenaudio frequency is generated.

It is desired in such a three-phase a.c. generator to prevent excessivecongregation of coil ends as far as possible and to make constant thedensity of the arrangement of the coil ends in a circumferentialdirection so that forced bending and large projection in a radial oraxial direction, for example, may be avoided.

The present embodiment aims at solving these problems and making itpossible to reduce a windage noise and excessive congregation of coilends.

To this end, in the present embodiment, a first set of three-phasearmature windings (X, Y and Z phases) and a second set of three-phasearmature windings (u, v and w phase) are inserted into odd and evennumbered slots, respectively. The spaces between the centers ofneighboring coil ends in a peripheral direction are arranged at a pitchpattern of 1, 2, 2, 3, 2, 2 times as large as a unit pitch.

The present embodiment is shown in FIGS. 11 to 13. FIG. 11 is a windingdiagram showing the windings of an armature FIG. 12 is a circuit diagramshowing the connection of the armature windings, and FIG. 13 is asectional view showing the main parts of the generator.

The three-phase a.c. generator for a vehicle includes rotor cores 12, 13having twelve claw poles in total mounted on a rotary shaft 11. Therotor cores 12, 13 have centrifugal fans 17, 18 disposed at oppositeends thereof. The rotor cores 12, 13 are rotatably supported inside thearmature core 20a. Coil ends of the three-phase armature windings 30protrude in both axial directions from the armature core 20a. Thearmature core 20a has 72 slots (indicated by reference numerals SLN 1through 72). Therefore, one slot space interval between adjacent slotscorresponds to electrical angle 30°.

As shown in FIG. 12, the three-phase armature windings 30 include afirst set of three-phase armature windings (X, Y, Z) and a second set ofthree-phase armature windings (u, v, w) which are connected in Y-formand are connected with independent three-phase full wave rectifiers 5and 6, respectively.

The three-phase armature windings (X, Y, Z) and (u, v, w) are wound withfull pitch in the order of X, −u, Z, −w, Y, −v, −X, u, −Z, w, −Y and v,as shown in FIG. 11. Here, the symbol, “−” designates a direction of awinding from the lower to upper side as viewed in the drawing.References M, M′ and N, N′ represent winding starting and endingterminal groups, respectively.

Accordingly, a voltage induced in each phase winding of the second setof three-phase armature windings (u, v, w) which are inserted in theeven numbered slots (which may be, of course, odd numbered slotsdepending upon the numbering of the slots) has a phase shift ofelectrical angle 30° from that of a given phase winding of the first setof three-phase armature windings (X, Y, Z) inserted in the odd numberedslots (the even number and the odd number may be interchanged dependingupon selection of the numbering of the slots).

If the windings are distributed in such a manner, the spaces between thecenters m, m of two coil ends, which are arranged adjacent to each otherin a peripheral direction, are arranged with a pitch pattern of 1, 2, 2,3, 2, 2 times as large as a unit pitch. In this case, one unit pitch isassumed as one slot interval.

As mentioned above, in the three-phase a.c. generator of this secondembodiment, as shown in FIGS. 11 and 14, respective phase windings (X,Y, Z, u, v, w) are arranged in the order of X, −u, Z, −w, Y, −v, −X, u,−Z, w, −Y and v.

Accordingly, excessive congregation of coil ends can be reduced ascompared with a comparative example illustrated in FIG. 15 in which thephase windings are arranged in the order of X, u, −Z, −w, Y, v, −X, −u,Z, w, −Y and −v.

In FIG. 14, a pair of coil ends extending to the right side afterdeparting upward from the slots 71 and 1 intersect with a pair of coilends extending to the left side after departing upward from the slots 2and 4 in the present embodiment of the three-phase a.c. generator shownin FIG. 14. Since the coil ends departing from the slots 2 and 4 areapart from each other by a distance of two slots, excessive congregationof coil ends is more difficult to occur as compared with the comparativeexample of FIG. 15, and hence the coil end treatment becomes easier.

Since the present embodiment adopts a cooling structure in whichcentrifugal fans 17, 18 are disposed beneath the coil ends to directcentrifugal air flow to the coil ends as shown in FIG. 13, high coolingefficiency especially at the coil ends may be maintained, while awindage noise, which has been inevitably produced at the coil ends, canbe removably reduced. In other words, since positional pitches of thewindings are made unequal as mentioned above, the convex and concavestates of the coil ends are also made unequal with the aforesaidpitches. Therefore, the frequency components of a noise produced at theconcave and convex portions are made to be dispersed and to be loweredin level over the range from a low frequency to a high frequency, sothat they arouse no unfavorable feeling to the ear.

Next, a third embodiment of the present invention is shown in FIGS. 16and 17. FIG. 16 is a winding diagram showing the armature windings, andFIG. 7 is a circuit diagram showing the connection of the armaturewindings.

In the present embodiment, a first set of three-phase armature windings(X, Y, Z) are connected in Y-form and a second set of three-phasearmature windings (u, v, w) are connected in a delta-form. Respectiveoutput terminals of both sets of armature windings are commonlyconnected with each other and are coupled to a.c. input terminals of athree-phase full wave rectifier 50.

Of course, the ratio of the number of turns of the first set ofthree-phase armature windings (X, Y, Z) to that of the second set ofthree-phase armature windings (u, v, w) is present to a given ratio.

However, the phase windings (X, Y, Z, u, v, w) are arranged in the orderof X, −u, Z, −w, Y, −v, −X, u, −z, w, −Y and v in the same way as thesecond embodiment.

The starting terminal groups M, M′ (X1, Y1, Z2, u2, v2, w1) and theending terminal groups N, N′ (X2, Y2, Z1, u1, v1, w2) of the two sets ofthree-phase armature windings are positioned so that the ending terminalZ1 is taken out from the slot 13 which is closest to the terminals u3and w1 with which the ending terminal Z1 is to be connected for thepurpose of easier connection.

A fourth embodiment of the present invention will now be described.

Generally, there have been a three-phase a.c. generators havingthree-phase armature windings which are connected in Y-form ordelta-form and which are wound concentratedly with full pitch on anarmature core having three slots per one-pole pitch. With such a type ofthree-phase a.c. generator, even if a phase current flowing through eachphase armature winding X, Y and Z is sinusoidal, the distribution of theair gap magnetomotive force remarkably fluctuates along thecircumference of the rotor due to an influence of the third harmoniccurrent contained in the armature current. Accordingly, the distributionof the air gap magnetomotive force is greatly distorted with themovement of a rotor in a rotational direction thereof, and, at the sametime, the distribution of the air gap magnetomotive force fluctuatesrelative to the magnetic poles of the rotor. Therefore, there has beenraised a problem that a noise is generated by the magnetic interactiveforce occurring between the air gap magnetomotive force distribution ofthe stator and the field magnetomotive force distribution of the rotor.

The reasons therefor will now be analyzed.

FIG. 22(a) shows changes with time of the magnetic motive forces (MMF)of respective windings AX, AY and AZ each of which is the product of thephase current of each of the armature windings X, Y, Z and the number ofturns of each of the armature windings X, Y, Z.

In FIG. 22(a), symbols t₂ and t₃ denote the time points which haveelapsed through electrical angle of π/6 rad from time points t₁ and t₂,respectively.

The air gap magnetomotive force distributions of respective windings attime points t₁, t₂ and t₃, which are obtained in consideration of thearrangement of the armature windings X, Y and Z shown in FIG. 22(b), areshown in FIGS. 22(c), 22(e) and 22(g), respectively.

Then, the resultant magnetomotive force distributions at time points t₁,t₂ and t₃, which are obtained by synthesizing the air gap magnetomotiveforce distributions of respective windings, are shown in FIGS. 22(d),22(f) and 22(h), respectively.

As seen from FIGS. 22(d) and 22(h), the resultant magnetomotive forcedistribution at time point t₁ is identical with that at time point t₃only with an exception that the identical resultant magnetomotive forcedistribution is shifted in a rotational direction of the rotor through arotational shift of the rotor (corresponding to electrical angle ofπ/3). However, the resultant magnetomotive force distribution at timepoint t₂ is greatly different from the distributions at time points t₁and t₃.

Thus, it is supposed that an electromagnetic noise is produced in theabove-mentioned three-phase a.c. generator due to the fact that themagnetic interactive force caused by the air gap magnetomotive forcedistribution of the armature windings of the stator to exert on thefield magnetomotive force distribution of the magnetic poles of therotor fluctuates, as viewed along the circumference of the rotor withthe movement of the rotor in a rotational direction thereof.

In order to reduce such an electromagnetic noise, in conventionalthree-phase a.c. generators, the following approaches have heretoforebeen adopted.

A sound insulation wall is provided on the outer side of the generatorto provide complete insulation from a noise. The shape of magnetic polesof a rotor is changed by providing the magnetic poles of the rotor withconvex portions so that the air gap may become nonuniform. The armaturewindings of the stator are wound distributedly and inserted inmulti-slots to make the air gap magnetomotive force distribution of thearmature windings sinusoidal. The magnetic poles are skewed or thepositions of N and S poles are shifted through one half wave length tomake magnetic pulsating forces of the magnetic poles or the armaturecore cancel each other.

However, these approaches encountered problems such as degradation ofoutput performance due to an increase in magnetic resistance of air gap,etc., rise of cost due to a decrease of the efficiency of assemblingwork, and an increase in size of product by the provision of a soundinsulating wall on the outside of a housing for a three-phase a.c.generator, and so on.

In order to solve the problems, the inventors have found that anelectromagnetic noise can be reduced, if the fluctuation of a reactiveelectromagnetic force applied to the rotor by the stator is decreased bypreventing a magnetic interactive force between the field magnetomotiveforce distribution and the air gap magnetomotive force distribution frombeing changed with the movement of the rotor in a rotational directionthereof, and, at the same time, have devised a structure of thegenerator which is able to reduce the number of rectifiers to be used.

In such a structure of the generator, a Y-connected three-phase circuithaving three first windings connected in Y-form and a delta-connectedthree-phase circuit connected in parallel with the Y-connectedthree-phase circuit and having three second windings, each having thenumber of turns 1.5 to 2.2 times as many as that of the three firstwindings, are inserted in a plural number of slots, with a phase shiftof electrical angle π/6 radians provided therebetween.

The reason why the number of turns of the second windings is made 1.5 to2.2 times as many as that of the first windings is that there is aproblem that a circulating current due to an unbalanced electromotiveforce is generated to give rise to power loss, if a different number ofturns other than that mentioned above is adopted.

As a result, third harmonic currents contained in the three firstwindings, respectively, and third harmonic currents contained in thethree second windings, respectively, coincide in phase with each other,since the first windings and the second windings having the number ofturns 1.5 to 2.2 times as many as that of the first windings areinserted in the plural number of slots.

Since the first and second windings are inserted in the plurality ofslots with a phase shift of electrical angle π/6 radians providedtherebetween, the currents flowing through the first and second windingsalso have the phase difference of electrical angle of π/6 radianstherebetween.

Accordingly, a comparison of a resultant magnetomotive forcedistribution at a given time point with that at the other time pointwhich has elapsed through a time corresponding to π/6 rad shows that theresultant magnetomotive force distribution having one and the same shapehas moved through electrical angle π/6 rad in a rotational direction ofthe rotor.

Therefore, since the magnetic interactive force between the fieldmagnetomotive force distribution and the air gap magnetomotive forcedistribution becomes constant irrespective of the position of the rotorin its rotational direction, no large pulsating force is generatedbetween the rotor and the stator. Hence, no large pulsed vibrating forceis generated between the rotor and the stator.

FIGS. 17 and 20 concretely show a fourth embodiment of the presentinvention. FIG. 17 is a circuit diagram showing the armature coil, FIG.18 is a view showing a development of armature windings of each phase,and FIG. 19 is a view showing the magnetic poles of the rotor.

The three-phases Y-connected circuit 51 is composed of three firstarmature windings X, Y, Z which are connected in Y-form to makeelectromotive forces of the windings have phase differences of 2π/3 fromeach other. The starting portion of the first armature winding X isconnected with the starting portions of the first armature windings Yand Z. The first armature windings X, Y and Z have substantially thesame number of turns, and they are wound concentratedly with full pitchin three-phases and are inserted in the slots of the armature core 20a.

The three-phase delta-connected circuit 52 is connected in parallel withthe three-phases Y-connected circuit 51 and comprises three secondarmature windings u, v, w, so that electromotive forces thereof have aphase difference of 2π/3 from each other. The second armature windingsu, v, w are wound concentratedly with full pitch in three-phases and areinserted in the slots of the armature core 20a in the same way as thefirst armature windings X, Y, Z.

The ending portions of the first and second armature windings X and uand the starting portion of the second armature winding v are connectedwith each other at one point to form a first terminal 53 for the twosets of three-phase windings. The ending portion of the first and secondarmature windings Y and v and the starting portion of the secondarmature winding w are connected with each other at one point to form asecond terminal 54 for the two sets of three-phase windings. The endingportions of the first and second armature windings Z and w and thestarting portion of the second armature winding u are connected at onepoint to form a third terminal 55 for the two sets of three-phasewindings.

The second armature windings u, v, w have substantially the same numberof turns, which is 3 times as many as that of the first armature windingX, Y, Z. The wire diameter of the second armature windings u, v, w issubstantially 1/{square root over (3)} times as large as that of thefirst armature windings X, Y and Z. Accordingly, the total sectionalarea of the windings inserted in each slot of the armature core 20a aresubstantially equal to each other.

Referring to FIG. 18, the armature core 20a is provided with 12 slotsper two pole pitches on the inner peripheral surface thereof opposite tothe rotor 10. That is, the armature core of this embodiment has slotstwice as many as those of an armature core of a usual a.c. generatorhaving concentrated three-phase full pitch windings. The two polepitches are a quotient of the division of the inner peripheral surfaceof the armature core by the number of magnetic poles, which quotientcorresponds to electrical angle 2π rad.

As mentioned above, the first and second armature windings X, Y, Z andu, v, w are inserted in the slots so that the second armature windingsare shifted from the first armature windings by electrical angle π/6 rad(=30°) in a rotational direction of the rotor.

In FIG. 19, the rotor cores 12 and 13 have substantiallytrapezoidal-shaped (Lundell type) claw poles and are supported insidethe armature core 20a to be opposite to the inner peripheral surface ofthe armature core and to be apart therefrom through an air gap which is,for example, about 0.35 mm. When the field winding 14 is energized, allthe claw poles 21a become N poles and all the claw poles 13a becomes Spoles. Since each of the claw poles 12a is disposed between the othertwo claw poles 13a, twelve N and S poles are disposed alternately alongthe outer periphery of the rotor cores 12, 13.

In FIG. 17, the three-phase full wave rectifying circuit 40 is composedof six diodes 41 through 46 and is connected with the first terminal 53,the second terminal 54 and the third terinal 55 at the junction pointsof the two sets of three-phase windings to rectify the a.c. currentsgenerated in the three-phase Y-connected circuit 52 and the three-phasedelta-connected circuit 52. The output of the three-phase full waverectifying circuit 40 is supplied to electrical apparatuses and a powersource battery via an output terminal 50.

The operation of the three-phase a.c. generator of the presentembodiment will be described with reference to FIG. 20. FIG. 20 is adrawing showing the air gap magnetomotive force distribution of; thefirst and second armature windings X, Y, Z and u, v, w, respectively.

FIG. 20(a) shows the change with time of the magnetomotive forces (MMF)AX, AY, AZ, Au, Av, Az of respective windings, each of which is aproduct of the phase current of each of the armature windings X, Y, Z,u, v, w and the number of turns of each of the armature windings X, Y,Z, u, v, w.

By the combined consideration of the air gap magnetomotive forces ofrespective windings at time points t₁, t₂ and t₃ shown in FIG. 20(a) andthe arrangement of the armature windings X, Y, Z, u, v, w shown in FIG.20(b), the air gap magnetomotive force distributions of respective setsof windings at time points t₁, t₂ and t₃ are obtained as shown in FIGS.20(c), 20(e) and 20(g). The resultant magnetomotive force distributions,which are obtained by synthesizing the air gap magnetomotive forcedistributions of respective sets of windings, have the same waveform attime points t₁, t₂ and t₃, as shown in FIGS. 20(d), 20(f) and 20(h), andthus they have a stationary wave relationship with respect to themagnetic poles 12a, 13a of the rotor.

That is, if the reaction system of the first and second armaturewindings X, Y, Z, and u, v, w is shifted by electrical angle π/6 rad andthe magnetic poles 12a and 13a of the rotor are rotated in a rotationaldirection through the same electrical angle, the resultant magnetomotiveforce distribution is obtained always by synthesizing the distributionsshown in FIGS. 20(d) and 20(f). Therefore, even when the rotor and theresultant magnetomotive force distribution are moved in a rotationaldirection passing the time points t₁, t₂ and t₃, the shape of theresultant magnetomotive force distribution does not change even afterthe air gap magnetomotive force of the armature has been subjected tothe reaction by the field magnetomotive force of the rotor, so that theresultant magnetomotive force distribution is only shifted with themovement of the rotor in a rotational direction.

Accordingly, since the interactive magnetic force occurring between thefield magnetomotive force distribution and the air gap magnetomotiveforce distribution remains constant irrespective of a rotationalposition of the magnetic poles 12a and 13a of the rotor, no remarkablepulsation is generated other than a magnetic pulsating force caused by aslight slot ripple occurring at the slot opening.

Thus, since no large pulsed vibrating force is generated between thearmature of the rotor, an electromagnetic noise can be reduce withoutrequiring any large scale sound insulating wall or any specialcountermeasure and without causing the output performance to bedeteriorated and the cost and size of a product to become high andlarge, respectively.

Since the fluctuation of the magnetic flux on the surface of themagnetic poles 12a and 13a of the rotor can be reduced, the outputefficiency of the a.c. generator can be elevated due to a remarkabledecrease in magnetic resistance. Further, a decrease in heat generationof the magnetic poles 12a and 13a can lower the temperature of the fieldwinding, so that the output efficiency of the a.c. generator can befurther improved due to the fact that a stronger exciting force can beutilized.

When a first set of armature windings X, Y, Z and a second set ofarmature windings u, v, w are inserted in the slots so that they areshifted by π/6 rad from each other, the output currents from therespective set of armature windings differ in phase from each other.Accordingly, two sets of three-phase full wave rectifying circuits 4 arerequired for an output load circuit. In order to solve this problem, itis devised to prevent unbalanced circulating currents from beinggenerated by making the ratio of the numbers of turns of the respectivewindings be 1:{square root over (3)}, by connecting a Y-connectedwinding set in parallel with a delta-connected winding set andsimultaneously by making the voltage and phase of each correspondingoutput terminal identical with each other between the respective windingsets. Since an output can be obtained by a single set of three-phasefull wave rectifying circuit 40, an inexpensive and compact a.c.generator can be provided.

Since the wire diameter of the first set of armature windings X, Y, Zand that of the second set of armature windings u, v, w are made to havea ratio of 1:1/3, the current density does not differ between the twowinding sets, so that the utilization efficiency of the wires is notdeteriorated. Since the total conductor sectional area of the first andsecond armature windings X, Y, Z and u, v, w within a slot, which isproportional to the number of turns multiplied by (the wire diameter)2,is substantially the same, the space utilization efficiency of the slotis not deteriorated.

FIG. 21 shows a fifth embodiment of the present invention in whichdiodes 47 and 48 are connected to a neutral point 56 of the three-phaseY-connected circuit 51. A third harmonic current contained in the outputof the three-phase Y-connected circuit 51 is taken out from the neutralpoint 56.

Although a three-phase full wave rectifying circuit has been used for anoutput load circuit, a rectifying circuit using a transistor bridge,Zener diodes, etc. may be used.

In the above-described embodiment, the ratio of the numbers of turns ofthe first and second sets of armature windings has been assumed as1:{square root over (3.)} However, it may be in the range of 1:1.5-2.2

We claim:
 1. An alternating current generator comprising a rotatablysupported field rotor having a pair of opposed rotor pole cores, eachbeing provided with P/2 claw poles wherein P is an even number; anarmature core located around the outer periphery of the field rotor andhaving axially extending 3nP slots wherein n is an integer more thanone; n independent sets of three-phase windings, each being wound on thearmature core by being inserted in the slots so that the n sets ofthree-phase windings are shifted from each other by an electrical angleof π/(3n) radians; and three-phase rectifiers connected with the n setsof three-phase windings to rectify output voltages generated by thethree-phase windings.
 2. An alternating current generator as set forthin claim 1, in which said claw poles have a trapezoidal peripheral shapeand P=12 and n=2 hold so that said armature core has 72 slots and saidthree-phase windings include first and second three-phase windings. 3.An alternating current generator as set forth in claim 2, in which thelength L of the base side of the trapezoidal peripheral shape of saidclaw poles is less than 7τ-A, wherein τdenotes a slot pitch of saidarmature core and A denotes the peripheral width of a tip end of a toothportion of said armature core.
 4. An alternating current generator asset forth in claim 2, in which said first and second three-phasewindings are substantially identical with each other in diameter of thecross-section of a winding conductor, the number of parallel windingconductors, and the number of winding turns.
 5. An alternating currentgenerator as set forth in claim 2, in which said first and secondthree-phase windings of each phase are wave-shaped windings having aplural number of parallel winding conductors.
 6. An alternating currentgenerator as set forth in claim 1, in which all the n sets ofthree-phase windings are connected in Y-form, respectively, and each setof three-phase windings has an independent three-phase rectifierconnected thereto, and direct current output terminals of the respectiverectifiers are connected in parallel with each other.
 7. An alternatingcurrent generator as set forth in claim 2, in which all the n sets ofthree-phase windings are connected in Y-form, respectively, and each setof three-phase windings has an independent three-phase rectifierconnected thereto, and direct current output terminals of the respectiverectifiers are connected in parallel with each other.
 8. An alternatingcurrent generator as set forth in claim 1, in which the n sets ofthree-phase windings are two sets of three-phase windings, with one setbeing connected in Y-form and the other set being connected indelta-form, and the two sets of three-phase windings are connected inparallel with each other and then connected to a common three-phaserectifier.
 9. An alternating current generator as set forth in claim 2,in which the n sets of three-phase windings are two sets of three-phasewindings, with one set being connected in Y-form and the other set beingconnected in delta-form, and the two sets of three-phase windings areconnected in parallel with each other and then connected to a commonthree-phase rectifier.
 10. An alternating current generator as set forthin claim 8, in which the number of turns of the delta-connectedthee-phase windings is 1.5 to 2.5 times as many as that of theY-connected three-phase windings.
 11. An alternating current generatoras set forth in claim 9, in which the number of turns of thedelta-connected three-phase windings is 1.5 to 2.5 times as many as thatof the Y-connected three-phase windings.
 12. An alternating currentgenerator as set forth in claim 2, in which said first and secondthree-phase windings are inserted in odd and even numbered slots of saidarmature core, respectively, and center portions of respective coil endsof each phase of said first and second three-phase windings projectingfrom both sides of said armature core are arranged with a pitch patternof 1, 2, 2, 3, 2, 2 times as large as a unit pitch in a peripheraldirection of said armature core.
 13. An alternating current generatorcomprising: a frame for defining an accommodation space therein; asubstantially cylindrical armature core rigidly supported in theaccommodation space of said frame and having a plurality of slotsaxially extending along an inner wall thereof; first and second sets ofthree-phase windings wound respectively being inserted in said pluralityof slots so that the respective sets of three-phase windings arearranged with a phase difference of electrical angle of π/6 radianstherebetween; a field rotor comprising: a field core having a pair ofopposed rotor pole cores and rotatably disposed inside and armaturecore, each of said rotor pole cores having P/2 claw poles wherein P isan even number; and a field winding wound around said rotor pole cores;and three-phase rectifiers connected with said first and second sets ofthree-phase windings for rectifying an output generated therefrom, saidclaw poles having a substantially trapezoidal peripheral shape, and saidarmature core having 6P slots.
 14. An alternating current generator asset forth in claim 13, in which the length L of the base side of thetrapezoidal peripheral shape of said claw poles is less than 7π-A,wherein π denotes a slot pitch of said armature core and A denotes theperipheral width of a tip end of a tooth portion of said armature core.15. An alternating current generator as set forth in claim 13, in whichboth said first and second sets of three-phase windings are connected inY-form, respectively, and each set of three-phase windings has anindependent three-phase rectifier connected thereto, and direct currentoutput terminals of the respective rectifiers are connected in parallelwith each other.
 16. An alternating current generator as set forth inclaim 14, in which both said first and second sets of three-phasewindings are connected in Y-form, respectively, and each set ofthree-phase windings has an independent three-phase rectifier connectedthereto, and direct current output terminals of the respectiverectifiers are connected in parallel with each other.
 17. An alternatingcurrent generator as set forth in claim 13, in which one set ofthree-phase windings is connected in Y-form and the other set beingconnected in delta-form, and the two sets of three-phase windings areconnected in parallel with each other and then connected to a commonthree-phase rectifier.
 18. An alternating current generator as set forthin claim 14, in which one set of three-phase windings is connected inY-form and the other set being connected in delta-form, and the two setsof three-phase windings are connected in parallel with each other andthen connected to a common three-phase rectifier.
 19. An alternatingcurrent generator as set forth in claim 17, in which the number of turnsof the delta-connected three-phase windings is 1.5 to 2.5 times as manyas that of the Y-connected three-phase windings.
 20. An alternatingcurrent generator as set forth in claim 18, in which the number of turnsof the delta-connected three-phase windings is 1.5 to 2.5 time as manyas that of the Y-connected three-phase windings.
 21. An alternatingcurrent as set forth in claim 13, in which said first and second sets ofthree-phase windings are inserted in odd and even numbered slots of saidarmature core, respectively, and center portions of respective coil endsof each phase of said first and second three-phase windings projectingfrom both sides of said armature core are arranged with a pitch patternof 1, 2, 2, 3, 2, 2 times as large as a unit pitch in a peripheraldirection of said armature core.
 22. The alternating current generatoras claimed in claim 1, wherein the alternating current generator is analternating current generator for a vehicle.
 23. The alternating currentgenerator as claimed in claim 22, wherein the alternating currentgenerator for a vehicle is adaptive to be driven by an engine of avehicle, and wherein the field rotor, the armature core, the three-phasewindings and the three-phase rectifiers are adaptive to supply electricpower to a vehicle battery and a vehicle load.
 24. The alternatingcurrent generator as claimed in claim 23, wherein the field rotor has afield winding, and wherein the alternating current generator comprises avoltage regulator which preforms conduction control of the field windingin response to the terminal voltage of the vehicle battery to regulatethe vehicle battery at a constant terminal voltage.
 25. The alternatingcurrent generator as claimed in claim 1, wherein each of said claw poleshas a trapezoidal peripheral shape, and only one tooth portion of saidarmature core may simultaneously overlap with two of said claw poles.26. The alternating current generator as claimed in claim 13, whereinthe alternating current generator is an alternating current generatorfor a vehicle.
 27. The alternating current generator as claimed in claim26, wherein the alternating current generator for a vehicle is adaptiveto be driven by an engine of a vehicle, and wherein the field rotor, thearmature core, the three-phase windings and the three-phase rectifiersare adaptive to supply electric power to a vehicle pattern and a vehicleload.
 28. The alternating current generator as claimed in claim 27,wherein the field rotor has a field winding, and wherein the alternatingcurrent generator comprises a voltage regulator which performsconduction control of the field winding in response to the terminalvoltage of the vehicle battery to regulate the vehicle battery at aconstant terminal voltage.
 29. The alternating current generator asclaimed in claim 13, wherein each of said claw poles has a trapezoidalperipheral shape, and only one tooth portion of said armature core maysimultaneously overlap with two of said claw poles.